In Third Generation Partnership Project (3GPP) systems, an internet protocol (IP) multimedia subsystem (IMS) network can provide mobile users with IP multimedia services, such as voice, video and data. Using IMS, a mobile device may transmit and receive multimedia and/or voice packet switched (PS) communications via a base station implementing one or more IMS Functional Components. To implement IMS, networks can rely upon session initiation protocol (SIP) to provide text-based signaling that can be used to communicate between a UE and the IMS Core Network (CN), between the IMS CN and Application Servers, and between various other components of the IMS Network.
In an IMS network, when a caller wishes to establish an IMS communication session with a callee, the caller's mobile device can construct a SIP INVITE request and forward it to the caller's home network via a Proxy-Call Session Control Function (P-CSCF). The P-CSCF can take a snapshot of the Session Description Protocol (SDP) in the INVITE request and routes the request further to the caller's Serving-SCF (S-CSCF). After receiving and validating the request, the S-CSCF retrieves the caller's initial Filter Criteria (iFC) from the Home Subscriber Server (HSS) and executes the service control logic. The execution logic may include, for instance, invocation of IMS Application Servers (ASs) located in the home network. Typically, the S-CSCF does not invoke the IMS AS by itself, but passes control over the service orchestration to a service broker Application Server (AS). In some instances, the service broker AS orchestrates the IMS AS invocations based on the iFC configurations.
Once the IMS AS has processed the SIP INVITE request, the control is returned back to the S-CSCF. The S-CSCF can determine a next hop for the request and forwards the request to the callee's Interrogating-CSCF (I-CSCF). The I-CSCF can locate the home S-CSCF of the callee and sends the request to the S-CSCF through a number of DNS and diameter queries. The IMS AS's invocation in the terminating network is similar to the originating. Further, the S-CSCF forwards the request to the callee's P-CSCF and finally the callee's mobile device receives the request. The response generated by the callee traverses the same path back to the caller. After several forward and back SIP messages, the session establishment procedure is completed.
Like reference symbols in the various drawings indicate like elements.